1. Field of the Invention
The present invention relates to a vehicle, in particular a bicycle, having at least one drive wheel, a motor which is connected to the drive wheel, a power accumulator for supplying the electric motor, a control unit for controlling the electric motor, and a pedal crank.
2. The Prior Art
Various vehicles are known which may be driven on one hand using muscle force and on the other hand using an auxiliary drive. These are typically electric bicycles, which have a pedal crank, which is connected via a drive chain to the rear wheel, and are additionally equipped with an electric motor, which may be used alternatively or additionally to the muscle drive. Such solutions have the disadvantage that in the event of mixed operation, the travel velocity is related only indirectly or not at all to the drive torque which is applied to the pedal crank. The driver of such a bicycle must therefore both control the electric motor via a regulator and also perform an appropriate adaptation of the pedal power to be able to produce the particular desired velocity as a function of slopes, gradients, and wind conditions. Furthermore, a bicycle is known from U.S. Pat. No. 3,884,317 A, which has an electric drive in the pedal crank, which drives a generator and is no longer connected to the wheels, however. In addition thereto, current may be fed from a battery into the system, so that the electric drive motor is partially supplied with the current which the driver generates via the pedal crank on the generator and partially by the current taken from the battery. Using such a bicycle, the travel velocity may be largely controlled by the power applied to the pedal crank within predefined limits. This results in simplified operation for the user in comparison to the prior solution. Through corresponding shifting of the generator, an attempt is made to produce an approximately natural behavior of such a bicycle in comparison to a mechanically driven vehicle, i.e., that the speed of the drive crank corresponds to the speed of the drive wheel within one gear setting. However, it has been shown that this requirement is only to be achieved to some extent in stationary or nearly stationary operation. In transition states, i.e., in transient operation, a bicycle of this type differs significantly from a typical bicycle, which has an unpleasant effect on the drivability.
To compensate for these existing disadvantages, in particular when starting, a solution has been suggested in WO 00/59773 A, in which the generator is activated by a control unit in such a way that a high resistance torque brakes the pedal crank when starting. In this way, the behavior of a vehicle may approach that of a mechanically driven vehicle. To be able to achieve sufficiently precise and realistic adaptation, a very high outlay is required for this solution, however, which particularly comprises complex power electronics for activating the generator. To be able to apply the appropriate resistance torques, the generator must be implemented as correspondingly large and high-performance. Such solutions have not been successful because of the required outlay.
A further known solution is described in EP 0 784 008 A. A generator is also driven by the pedal crank here to obtain electrical current for the propulsion of a bicycle. Additional current sources such as a generator driven by an internal combustion engine, solar cells, or rechargeable batteries may also be provided here. This solution also requires complex power electronics to be able to appropriately control the torque to be applied to the generator on one hand and the drive on the other hand.
The object of the present invention is to refine a vehicle of the type described above in such a way that simulation of the behavior of a mechanically driven vehicle which is as realistic as possible may be achieved at acceptable outlay.
A further object of the present invention is to produce largely natural behavior of such a vehicle in comparison to a mechanically driven vehicle, i.e., within one shift setting, the speed of the pedal crank is related to the travel velocity in a way comprehensible to the user of the vehicle. It has been shown that in particular with high-performance drives in transition states, i.e., in transient operation, high oscillations of the drive torque are to be observed, which negatively influence the driving behavior. Such oscillations are to be largely avoided with the solution according to the present invention.